1. Field of the Invention
The present invention relates to a communication device, and more particularly, to an ATM-based data transmitting and receiving device.
2. Background of the Related Art
Generally, asynchronous transmission mode (ATM) is a packet-oriented transmission mode using an asynchronous time division multiplexing technology. A packet is called a cell and has a fixed size.
An example of an ATM cell is shown in FIG. 1. The ATM cell consists of 53 bytes. The header is 5 bytes and the remaining 48 bytes are a payload in which data to be transmitted is loaded. The header includes two quantities, a Virtual Path Identifier (VPI) and a Virtual Channel Identifier (VCI) that are used to recognize an ATM network connection in which cells are transmitted. The VPI represents a main path set between two exchange nodes and the VCI represents one specific connection portion on each main path.
Referring to a protocol standard model, ATM comprises a physical layer, ATM layer, ATM adaptation layer (AAL) and a higher layer. The ATM layer supports various kinds of services, which have different traffic characteristics and different system requirements. To accomplish this, applications of other classes are adapted. It is the AAL that performs this function.
The AAL is classified into four classes according to types of service. In other words, the classes are AAL1, AAL2, AAL3, AAL4 and AAL5. Among them, AAL3 and AAL4 are combined into AAL3/4. Referring to AAL3/4, this class is made for a service that needs variable speed for both of connection-oriented and non-connectional services. Originally, The AAL3/4 was divided into AAL3 and AAL4 but these two classes are combined into one AAL, i.e., AAL3/4.
AAL5 is a class that supports a connection-oriented service that has a variable transmission rate. The AAL5 is a simplified version of AAL3/4. In the AAL5, error correction and retransmission functions are omitted. Accordingly, the overhead portion of the bandwidth is reduced, process requirements are simplified and complexity of configuration is reduced.
The above-mentioned AAL is divided into a convergence sublayer (CS) and a segmentation and reassembly (SAR) sublayer. The CS is divided into common part CS (COCS) and service specific part CS (SSCS).
FIG. 2 illustrates a related art ATM-based data transmitting and receiving device. Referring to FIG. 2, the related art data transmitting and receiving device includes a first calculation processing module 10 for dividing a message to generate and transmit ATM cells. An ATM switch module 20 is used for switching the ATM cells received from the first calculation processing module 10 to the corresponding path using the VPI/VCI. A second calculation processing module 30 is used for receiving the switched ATM cells and restoring a message. Each of the first and second calculation processing modules 10 and 30 can generate ATM cells from the message and restore the message from the ATM cells. Accordingly, the second calculation processing module 30 can also generate ATM cells from the message and transmit them to the ATM switch module 20. Likewise, the first calculation processing module 10 can also restore the message from the ATM cells received from the ATM switch module 20.
In this manner, each calculation processing module of the related art data transmitting and receiving device divides the message, generates ATM cells, and restores the message from the ATM cells. Accordingly, if these calculation processing modules are employed in a communication network, the calculation processing modules can be a bottleneck due to the limited processing capability and large processing load from receiving and processing messages from a large number of nodes.